Electromagnetic coil



July 21, 1942. E. E. FRANZ ELECTROMAGNETIC COIL Filed March 13, 1940FIG. 2

INVENTOR E. E. FRANZ will Patented July 21, 1942 ELECTROMAGNETIC COILErwin E. Franz, Cranford, N. J., assignor to Western Electric Company,Incorporated, New York, N. Y., a corporation of New York ApplicationMarch 13, 1940, Serial No. 323,713

1 Claim.

This invention relates to electromagnetic coils and more particularly toelectromagnetic coils having one or more windings upon a toroidal core.

Toroidal coils have a great variety of applications in the electricalarts and especially in the arts of electrical communication. Especiallyin the field of telephony are such coils used in great numbers and inmany ways. It becomes, therefore, a matter of material importance bothto improve the electrical efficiency and reliability and to reduce themass, bulk and cost of such coils.

An object of the present invention is to produce a toroidal coil capableof manufacture in a simple, inexpensive and rapid manner, having arugged, compact and simple structure, and of enhanced reliability,constancy and efficiency of electrical properties.

With the above and other objects in View, one embodiment of theinvention may present a toroidal core consisting of a ribbon of magneticmaterial wound spirally into an annulus and radially slotted to permitof sliding the segments to adjust the width of the gap, an annular rigidsheath of non-magnetic material preformed to contain the core and retainits segments in place, and one or more conductor windings upon thesheath.

Other objects and features of the invention will appear from thefollowing detailed description of one embodiment thereof, taken inconnection with the accompanying drawing in which the same referencenumerals are applied to identical parts in the several figures and inwhich Fig. 1 is a broken plan view of a coil constructed in accordancewith the invention;

Fig. 2 is a sectional View on the line 2-2 of Fig. 1;

Fig. 3 is a plan view of the core slotting fixture with a slotted coretherein;

Fig. 4 is a broken plan view of a slotted core with its segmentsdisplaced for adjustment of the gap, and

form an annulus as shown. This may be conveniently done by winding theribbon or tape flatwise around a mandrel of suitable size. The materialof the ribbon, according to the purpose for which the coil is intended,will be of an appropriate magnetic alloy. Thus for a loading coil ortransformer, the core will preferably be of one of the recentlydiscovered high permeability, low retentivity alloys such as thatcommercially known as Permalloy and consisting, for example, of 79%nickel, 17% iron and 4% molybdenum. A temporary retainer ring or band II(Fig. 5) is then slipped over the coiled core to retain its turns inplace and the core in the ring is annealed to restore the magneticproperties damaged by the cold working effected by the windingoperation. The retainer ring II will be preferably of the same materialas the core in order to have the same coefiicient of thermal expansionand to avoid alloying of the core, although in some instances othermaterial may be used.

The wound and annealed core is then radially slotted. This mayconveniently be accomplished by transferring the core from the ring IIto a slotting fixture I2 such as is shown in Fig. 3. This fixtureconsists essentially of two suitably recessed jaws I4 and I5, pivotedtogether at I6. Stop shoulders at H prevent closing together of the jawsbeyond the position shown. Opposite the pivot, the jaws are formed toleave a parallel side slot I8 through which a suitable saw may enter tocut, the slot I9 radially through one side of the annular core. Withsuitable care and sharp tools, the slot I9 may be cut in the core withonly extremely localized and negligible damage to the magneticproperties of the core.

The slotted core is then transferred from the slotting fixture I2 to oneof the two matching annular cups 2I and 22 which together constitute thehollow toroidal body of the sheath 2%, e. g. to the cup 2I as shown inFig. 4. If desired, the effective width of the slot or gap I9 may now bediminished to practically any desired extent by successively displacingthe segments of the core within each other from their relative positionof Fig. 3 to some such relative arrangement as shown in Fig. 4. Thisobviates any necessity for a great variety of fixtures I2 andcorresponding saws to produce cores having gaps I9 of a variety ofeffective widths. The core gap having thus been suitably adjusted, theother sheath cup 22 is placed in position on the core; and the sheathedcore is then ready for winding. Preferably the wound core afterannealing and after slotting comes from the fixture I2 minutely largerin external diameter or smaller in internal diameter than thecorresponding annular recess in the cup 21 and has to be sprung a verylittle, Well Within its elastic limit, to fit it into the cup. Themutual friction between the core and the cups and between the successivesegments of the core will then retain the gap I9 safely at its adjustedwidth.

The cups 2! and 22 as shown have each a semi-toroidal body with anannular recess to receive the core, and are also formed with integralfins or winding separators 23 and 24 respectively extending radiallyinwardly and outwardly and also laterally outwardly from the body ofeach. Each fin on one body matches a corresponding fin on the other, sothat the two fins when placed in alignment as shown form a Windingseparator extending substantially entirely around the body. The two cupbodies may be so dimensioned that their opposed edges are spaced apartas shown in Fig. 2, or they may be dimensioned to have these edges abutand enclose the core completely.

Preferably the two sheath halves or cups 2! and 22 are preformed, e. g.by molding, from any appropriate and suitable non-magnetic andelectrically non-conductive material, such, for example, as artificialresin, casein plastic, cellulose plastic, glass, ceramic material, wood,paper pulp, or the like generally.

Preferably also metallic terminal members 25 and 25 may be mounted inthe outer ends of the fins 23 and 2 1, being molded directly andpermanently in place when the sheath cups are made by molding. Thus thecompleted coil will have terminal members not only well adapted forelectrically connecting the windings of the coil as desired, but whichare also sufiiciently mechanically rigid and strong to serve asmechanical supports by which the coil may be mounted without extraneousclamps, slings or the like.

Insulated electrical conductors are then wound on the sheathed core inany suitable manner to form the windings 3c, the ends of the windingsbeing attached to the several terminals in whatever arrangement isdesired as indicated at 3!. An outer weather covering 32 of suitablematerial, e. g. impregnated paper tape, may be placed over the windings,if necessary. If the winding of the sheathed core be done in a machinefor winding toroidal coils, the fins on the sheath may be used asmembers to locate a core in the machine for winding, quickly andaccurately.

While the coil disclosed herein as. an illustrative embodiment of theinvention has four sets of fins intercalated between four windings, theparticular number of fins and windings is not a characteristic of theinvention. There may be any desired number of these elements. In a verysimple form there may be no fins at all. In this last case there may bea single winding only, or more than one without any separating septasuch as the fins shown. In another simpler modification it may bedesired to omit the slot or gap l9, the continuous spiral core beingthen a very little overwound after annealing to be placed whole into thecups 2| and 22.

The embodiment disclosed is illustrative only and may be variouslymodified and departed from without departing from the spirit and scopeof the invention as pointed out in and limited solely by the appendedclaim.

What is claimed is:

An electromagnetic coil including an annular core consisting of aspirally wound ribbon of elastically deformable magnetic material andhaving a radial slot through one side thereof to render the segments ofthe ribbon slidable with respect to each other to adjust the magneticWidth of the slot and to render the core as a whole elasticallydeformable to alter the diameter thereof, a sheath enclosing the sameand comprising a plurality of members preformed of nonmagnetic andelectrically non-conductive material and each formed with an arcuaterecess of diameter a little difierent from the normal diameter of thecore to receive and elastically deform and substantially enclose thecore and to retain the segments thereof elastically in place whenadjusted relatively to each other, and. a winding of electricalconductor strand upon the sheath and separated thereby from the core.

ERWIN E. FRANZ.

